In the engine compartment of motor vehicles, a high number of individual sound insulations are mounted today. Essentially, these are referred to as the hood, dashboard and tunnel sound insulations as well as the undershield with absorber, the design cover with absorber and the acoustically effective heat shields. Recently, the textile wheel house panels have also been included in this group. In terms of material construction, the sound insulations are classified into mere absorbers, mass absorber systems, spring-mass systems and sandwich components in general. As absorber materials, temperature-resistant covering fleeces, PUR lightweight/cut foams, melamine resin foam, flock composite foam and single-fiber or mixed-fiber fleeces, in part in combination. As damping materials, highly filled PUR foams, integral foams, EVA/PE/PP/EPDM heavy sheets and TPE/TPO injection-molded parts are employed, which are in turn combined with the absorber materials. The design covers are mostly PA injection-molded parts, and the acoustically effective heat shields are usually sandwich components consisting of microperforated aluminum foil, rock wool, foam and single-fiber or mixed-fiber fleece.
DE 198 21 532 A describes a heat-insulating and soundproofing lining for the engine compartment of motor vehicles, especially for the dashboard or tunnel, consisting of covering fleeces on two sides with acoustically insulating foam or fleece layers sandwiched between. The bonding of the layers is achieved by adhesive layers. It is described that a metal foil is arranged on the engine side partially or on the whole area for heat protection.
DE 199 59 089 A describes that a convection channel for a gas fluid is additionally provided between the layers, and that the application thereof is intended, in particular, for hood insulation or dashboard lining.
WO 98/46456 A describes that the cavities are configured as lambda/4 resonators in an engine hood sound insulation, which is also employed for forming a heat shield.
Another resonator application in the hood in the form of a tube closed on one side is described in DE 197 55 750 A. A sound-absorbing cover with an absorber consisting of a plastic shell and foam materials provided between foam cover layers is described in DE 199 04 986 A. Shell decouplers for decoupling such design covers on vibrating parts, such as internal combustion engines, are described in DE 198 24 905 A. WO 2004/090307 describes an aggregate cover in the engine compartment of a motor vehicle consisting of a support part and a molded part of a sound-absorbing material integrally connected therewith.
DE 197 22 037 A describes a heat shield with a sound insulation in which a defined air gap is provided between the heat shielding plate and a support layer comprising the sound absorption layer facing the heat and sound source.
An acoustic cover that partially or completely covers the engine compartment on its upside and is integrated into these functional or control components of the internal combustion engine is described in DE 198 25 739 A.
A sound insulation plate mounted near the engine within the engine compartment for damping the engine noise is described in DE 198 47 441 A; a sound-absorbing material is provided on the top and bottom sides thereof.
DE 100 34 301 A describes a sound-insulated housing consisting of a light metal foam and plastic sandwich structure; the plastic material is preferably an elastomer material. A vibration-damping and sound-absorbing part consisting of a foam body and a stiff portion is described in DE 197 39 778 A. Said foam body is on the vibrating region of the vehicle part, and the stiff portion is outside. The utility model specification DE 20 2004 020 028 U describes a sound absorber for motor vehicle engines consisting of a self-supporting component and a sound-absorbing element and being positioned between the engine and radiator with the sound-absorbing element facing towards the engine.
The mentioned prior art does not relate to an acoustically and thermally effective insulation of an internal combustion engine. These sound insulations do not have a “closed” capsule effect; they are mounted as separate parts (mutually open to sound). On the other hand, sufficiently known material combinations are described in their relative position.
DE 198 18 859 A describes a noise capsule for the exhaust gas system that is designed and born in a way elastically compliant towards a force acting from below. This capsule does not have an absorptive and thermal effect either.
A foam with integrated thermoplastic substances is described in EP 1 184 149 A for soundproof covering. Urethane is mentioned as a foam, and polystyrene and styrene-acrylate copolymer are mentioned as thermoplastic substances.
A (thermally stable) polyurethane foam is also used in DE 199 35 335 A for encapsulation. The foam is directly foamed and applied to the engine, or applied as a self-supporting molded part or as a self-supporting composite part. See also the press release BASF P433 6./.10.03 “Thermische Motorkapselung mit PUR-Schaum—ein Weg zu weniger Kraftstoffverbrauch and mehr Verkehrssicherheit” in Polymers in the Automotive Industry, Vol. 1, Nos. 11+12/03, p. 14.
EP 1 029 742 A also describes a polyurethane foam for insulation; in particular, surface-active agents are employed. The foam is partially localized in the engine compartment, not as a capsule.
However, these designs can no longer be employed near the engine due to the temperature conditions in current engine compartments under the aspect of heat management; also, there is no purposeful coupling of acoustic and thermal insulation.
The sound-protection capsule described in DE 199 10 516 A consists of a housing and an adsorption layer applied to the inside thereof. In its material construction, the housing consists of several layers having a high modulus of elasticity; the layers themselves are interconnected by damping layers. As the materials, aluminum sheets are mentioned for the housing, and double-sided adhesive sheets are mentioned for the damping layers. The absorber layer consists of open-pore foam, fleece or basalt rock wool.
The sound absorption device for an engine compartment cover according to DE 100 25 826 A consists of several sound absorption plates respectively provided with a center part having sound-reflecting properties and with sound absorption elements attached to both lateral surfaces of the center part. These plates are juxtaposed near the aeration slots of the cover.
EP 0 921 291 A describes a driving capsule of a vehicle in which individual capsule elements with acoustic insulation are selectively connected by special connection channels. These channels and other guiding aids effect the supply and circulation of cooling air.
DE 199 14 934 A describes a sound-damped machine housing in which the noise encapsulation includes separate chambers closed in themselves and formed by tub-like regions integrated into the outer wall and closed by caps. The caps are connected with the edges of the tub-like regions by bonding with a permanently elastic adhesive to decouple vibrations and to seal them all around. At least some of the caps are designed as multipart bodies with a sound-damping intermediate layer. An assembly for damping the sound emitted by an engine/pump aggregate with a sound-damping cover for the engine/pump aggregate is described in DE 199 60 224 A. The cover is designed as a sound-damping hood that is put over the engine/pump aggregate without touching it.
DE 100 06 618 A describes a noise capsule partially formed from hollow spaces flowed through by coolant medium. This capsule consists of a plastic material and encloses part of the internal combustion engine. A sound-insulating housing with a special circulation of cooling water and air is described in EP 0 935 058 A. A damping capsule with noise-absorbing elements is described in DE 195 43 495 A. The absorption material is arranged along the sound path with varying thickness. An internal combustion engine encapsulated to insulate sound is described in DE 10 2004 017 362 A. In this case, the hood is provided with a sound absorption element; a pedestrian-protecting deformation element is arranged between the hood and the sound absorption element.
This prior art does not relate to a capsule having a thermal effect or the purposeful coupling of acoustic and thermal insulation.
This also applies to the engine compartment of a motor vehicle as described in DE 10 2004 028 593 A in which heat-shielding components are described in their position relative to one another and to the parts to be protected.
DE 103 24 257 B3 relates to a sound absorber consisting of two interconnected textile fiber fleeces (1, 2) bonded with a thermoplastic and/or thermosetting adhesive wherein the textile fiber fleece (1) facing towards the sound emission source has a layer thickness within a range of from 2 to 15 mm, a density within a range of from 50 to 500 kg/m3, a basis weight within a range of from 0.1 to 5 kg/m2, and a flow resistance within a range of from 50 to 1000 kNs/m4, and the textile fiber fleece (2) facing away from the sound emission source has a layer thickness within a range of from 10 to 100 mm, a density within a range of from 20 to 100 kg/m3, a basis weight within a range of from 0.5 to 1 kg/m2, and a flow resistance within a range of from 10 to 40 kNs/m4, with a total thickness of the sound absorber within a range of from 12 to 30 mm and a total basis weight of the sound absorber within a range of from 0.5 to 3 kg/m2.
In principle, all the components in the automobile industry must be judged by their contribution to the constantly increasing demands in terms of economic efficiency in fuel consumption and environmental compatibility. With respect to insulating or damping molded parts, the focus in this respect had been primarily to achieve weight reduction and/or recyclability of the molded parts or materials.
It is known that internal combustion engines are subject to an increased fuel consumption and wear in the cold running phase. Therefore, it is altogether usual in the prior art that the cooling of the engine cooling circulation or the withdrawal of engine heat for heating purposes in the passenger compartment is started only after a particular temperature of the engine has been achieved. In contrast, a thermally insulating engine encapsulation has not been considered because of the problems necessarily involved.
Namely, in addition to the expected high weight, engine encapsulations have basically the problem of having a high impact on the acoustic reactions within the engine compartment and thus on the noise level within the passenger compartment and outside the vehicle (“pass-by noise”).